Field of the Invention
The invention relates to semiconductor technology, and in particular to a semiconductor device with low gate charge capability.
Description of the Related Art
Lateral diffused metal-oxide-semiconductor field-effect transistors (LD-MOSFETs) have high voltage handling capacity. The trends of power saving and high speed performance affect LD-MOSFET structures. Currently, LD-MOSFETs with lower leakage and on-resistance (Ron) have been developed by many semiconductor manufacturers. Breakdown voltage is taken into account when an LD-MOSFET with low on-resistance is developed.
In general, the higher breakdown voltage that LD-MOSFETs sustain, the higher capacitance the LD-MOSFETs have. One of factors affecting the gate capacitance of LD-MOSFETs is the overlapping area between a gate and a drain region. For example, FIG. 1 shows a cross-sectional view of a conventional LD-MOSFET. The conventional LD-MOSFET comprises a substrate 100. A body region 160 and a drain region 170 are located in the substrate 100. An oxide layer 120, a gate dielectric layer 130 and a gate-electrode layer 140 are sequentially disposed on the substrate 100. The total gate-to-drain capacitance of the conventional LD-MOSFET includes a first gate-to-drain capacitance Cgd1 and a second gate-to-drain capacitance Cgd2 that correspond to the overlapping area between the gate-electrode layer 140 and the drain region 170.
However, conventional LD-MOSFETs usually have high total gate-to-drain capacitance (also referred to as parasitic capacitance), such that the switching speed of the power MOSFET is limited. Even if the parasitic capacitance is decreased, the power MOSFET is unable to work well in high-frequency applications.
Thus, there exists a need in the art for development of a semiconductor device and methods for forming the same capable of mitigating or eliminating the aforementioned problems. Therefore, embodiments of the invention provide a power MOSFET with lower total gate charge (Qg) and lower gate-to-drain capacitance, and able to work well in high-frequency applications.